Printed circuit board comprising metal bump and method of manufacturing the same

ABSTRACT

Disclosed herein is a printed circuit board, including: an upper circuit layer including connection pads made of a conductive metal and buried in an insulation layer; and metal bumps, each having a constant diameter, which are integrated with the connection pads and protrude over the insulation layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2008-0124154, filed Dec. 8, 2008, entitled “a printed circuit boardcomprising a metal bump and a method of manufacturing the same”, whichis hereby incorporated by reference in its entirety into thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board comprising ametal bump and a method of manufacturing the same, and, moreparticularly, to a printed circuit board comprising metal bumps, themetal bumps having constant diameters and arranged at fine pitches, anda method of manufacturing the same.

2. Description of the Related Art

With the advancement of electronics industry, electronic parts havebecome highly functionalized, and thus a package (PKG) is required to beminiaturized and highly-densified. Further, an interposer (substrate)for connecting an IC to a main board is also required to behighly-densified. The densification of the package is caused by theincrease in the number of I/Os, and methods of connecting the packagewith the interposer have improved. Currently, as a method of mounting anIC in a high-density package, a wire bonding method and a flip bondingmethod are used. Among them, the flip bonding method may be used due tothe costs required to mount the IC when the number of I/Os is increased.

FIG. 1 is of sectional views showing a conventional process ofmanufacturing a substrate on which a semiconductor chip is mounted.

First, as shown in FIG. 1A, a carrier 1 formed of a double-sided copperclad laminate is provided, and then, as shown in FIG. 1B, a solderresist 3 is applied on the carrier 1, and then, as shown in FIG. 1C, adry film 5 is applied on the solder resist 3 and then patterned.Thereafter, as shown in FIG. 1D, electrolytic plating is conducted, andthen, as shown in FIG. 1E, the dry film 5 is removed to form connectionpads 7. Subsequently, as shown in FIG. 1F, a first insulation layer 9 isformed on the connection pads 7 and the solder resist 3, and then, asshown in FIG. 1G, a first circuit layer 11 is formed.

Thereafter, as shown in FIG. 1H, a build-up layer 13 is additionallyformed by repeating the above processes, and then, as shown in FIG. 1I,a solder resist 15 is applied on the build-up layer 13.

Subsequently, as shown in FIG. 1J, the carrier 1 is separated byconducting a routing process, and then, as shown in FIG. 1K, copper foilis etched and removed. Then, as shown in FIG. 1L, the solder resists 3and 15 are patterned to form openings 17 for exposing the connectionpads 7.

Thereafter, as shown in FIG. 1M, solder balls 19 for flip chip bondingare formed in the openings 17. The formation of the solder balls 9 isconducted through a solder paste printing process using screen printingand a reflow process.

However, as described above, the method of forming a bump on a printedcircuit board using a printing process is problematic in that largeconnection pads are required, and thus it is difficult to realize bumparranged at fine pitches of 120 μm or less.

Further, the method of forming a bump on a printed circuit board using aprinting process is problematic in that a fine bump is not formed, orits volume is very small even though the fine bump is formed.

Further, in the method, since the connection pads are formed by plating,their thicknesses are different from each other due to platingdeviation, and, since solder paste cannot be easily printed in acompletely uniform manner even in the solder paste printing process, theheights of solder balls are not uniform, so that there is a problem inthat solder balls which are not connected to a semiconductor chip areformed.

Further, in the method, since the stepped portion of the solder resist15 is large, there is a problem in that voids are formed in an underfillprocess performed after the mounting of an electronic part.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the aboveconventional problems, and the present invention provides a printedcircuit board comprising metal bumps, the metal bumps arranged at finepitches and uniform diameter and height, and a method of manufacturingthe same.

An aspect of the present invention provides a printed circuit board,including: an upper circuit layer including connection pads made of aconductive metal and buried in an insulation layer; and metal bumps,each having a constant diameter, which are integrated with theconnection pads and protrude over the insulation layer.

In the printed circuit board, each of the connection pads may have anexposed surface being flush with a surface of the insulation layer.

The insulation layer may be made of a solder resist.

The printed circuit board may further include a connection metal layerformed on the metal bumps.

The printed circuit board may further include a build-up layer includinga lower circuit layer disposed beneath the insulation layer.

The lower circuit layer may include lower connection pads, and theprinted circuit board may further include a solder resist layer coveringthe lower circuit layer and having openings for exposing the lowerconnection pads.

Another aspect of the present invention provides a method ofmanufacturing a printed circuit board, including: applying a dry film ona carrier and then patterning the dry film to form holes for formingmetal bumps; forming an upper circuit layer including metal bumpscharged in the holes and connection pads on the dry film; forming aninsulation layer on the dry film; forming a build-up layer including alower circuit layer on the insulation layer; removing the carrier; andremoving the dry film.

In the method, the forming of the upper circuit layer may include:forming a seed layer on the holes and the dry film; patterning the seedlayer to form openings for forming the upper circuit layer, includingopenings for forming the connection pads, the openings exposing theholes; plating the openings for forming the upper circuit layer to formthe upper circuit layer including the metal bumps and the connectionpads; and removing the seed layer.

The method may further include: forming a solder resist layer on thelower circuit layer after the forming of the build-up layer.

In the method, the removing of the carrier may include: separating ametal foil constituting an outer layer of the carrier from the carrier;and removing the metal foil from the dry film.

The method may further include: forming a connection metal layer onbottoms of the holes after the applying of the dry film.

Various objects, advantages and features of the invention will becomeapparent from the following description of embodiments with reference tothe accompanying drawings.

The terms and words used in the present specification and claims shouldnot be interpreted as being limited to typical meanings or dictionarydefinitions, but should be interpreted as having meanings and conceptsrelevant to the technical scope of the present invention based on therule according to which an inventor can appropriately define the conceptof the term to describe the best method he or she knows for carrying outthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A to 1M are sectional views showing a conventional process ofmanufacturing a substrate on which a semiconductor chip is mounted;

FIGS. 2 to 11 are sectional views showing a method of manufacturing aprinted circuit board including a metal bump according to an embodimentof the present invention; and

FIGS. 12 to 22 are sectional views showing a method of manufacturing aprinted circuit board including a metal bump according to anotherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings.

Throughout the accompanying drawings, the same reference numerals areused to designate the same or similar components, and redundantdescriptions thereof are omitted. In the following description, theterms “upper”, “lower” and the like are used to differentiate a certaincomponent from other components, but the configuration of suchcomponents should not be construed to be limited by the terms.

FIG. 11 is a sectional view showing a printed circuit board including ametal bump according to an embodiment of the present invention. As shownin FIG. 11, the printed circuit board according to an embodiment of thepresent invention includes an upper circuit layer 600 includingconnection pads 630 buried in an insulation layer 700 and made of aconductive metal; and metal bumps 500, having constant diameters, whichare integrated with the connection pads 630 and protrude over theinsulation layer 700.

The insulation layer 700 may be a solder resist layer, and may be madeof a composite polymer resin which is generally used as an interlayerinsulation material. For example, the insulation layer 700 may be madeof prepreg, or an epoxy resin such as FR-4, BT(Bismaleimide Triazine),ABF(Ajinomoto Build up Film) or the like, but the present invention isnot limited thereto.

The metal bumps 500 protrude over the insulation layer 700, and functionto electrically connect an electronic part to be mounted in the printedcircuit board later with wires formed in the printed circuit board. Themetal bumps 500 are integrated with the connection pads 630 buried inthe insulation layer 700, and are made of the same material as theconnection pads 630. Therefore, the metal bumps 500 are not completelydistinct from the connection pad 630, but the metal bumps 500 havediameters smaller than those of the connection pads 630 and protrudeover the insulation layer 700. In this embodiment, each of the metalbumps 500 has a post shape in which its upper diameter is the same asits lower diameter. Here, the meaning that the metal bump 500 has aconstant diameter does not mean that the upper and lower diameters ofthe metal bump 500 are mathematically exactly equal to each other butmeans that a slight change in diameter of the metal bump 500 due to theerrors occurring in a substrate manufacturing process is allowed.

In this case, a connection metal layer 410 may further be formed on themetal bumps 500. The connection metal layer 410 may be made of aconductive metal such as tin (Sn), an alloy of tin (Sn) and silver (Ag)or the like.

The upper circuit layer is buried in the insulation layer 700, andincludes the connection pads 630 integrated with the metal bumps 500. Inthis embodiment, the connection pads 630 are buried in the insulationlayer 700, but they have exposed surfaces which are exposed to theoutside of the insulation layer 700. Here, the exposed surfaces aresurfaces of the connection pads 630 which are not covered by theinsulation layer 700, and are not surfaces which are exposed to theoutside of another insulation layer or a solder resist layer which canbe formed on the insulation layer 700. In this embodiment, the exposedsurfaces of the connection pads 630 are flush with the surface of theinsulation layer 700. The connection pads may be made of a conductivemetal such as gold, silver, copper, nickel or the like.

Meanwhile, in this embodiment, only the upper structure of the printedcircuit board, which is a characteristic structure of the presentinvention, is described, but the printed circuit board according to theembodiment of the present invention further includes a build-up layer800 which is disposed beneath the insulation layer 700 and includes alower circuit layer 830 electrically connected to the upper circuitlayer 600. The build-up layer 800 may further include an inner circuitlayer 810 (refer to FIG. 7) formed between the upper circuit layer 600and the lower circuit layer 830. In this embodiment, only a single innercircuit layer 810 is exemplified, but the number of inner circuit layers810 is not limited thereto. It is easily understood by those skilled inthe art that, if necessary, the number of the inner circuit layers 810can be controlled.

In this case, the lower circuit layer 830 may include lower connectionpads, and may further include a solder resist layer 850 covering thelower circuit layer 830 and having openings 855 for exposing the lowerconnection pads.

According to the above printed circuit board, since the printed circuitboard includes the post-shaped metal bumps 500 having excellent electricconductivity, the printed circuit board can be easily connectedelectrically to an electronic part mounted therein.

Further, the above printed circuit board is advantageous in that theprinted circuit board includes metal bumps 500 arranged at fine pitchesbecause the metal bumps 500 have constant diameters, the lower diametersof which are not larger than the upper diameters thereof.

Furthermore, the above printed circuit board is advantageous in thatvoids are not formed in an underfill process because the height of theinsulation layer is the same as the height of the connection pads andthus a stepped portion is not formed therebetween.

FIGS. 2 to 11 are sectional views showing a method of manufacturing aprinted circuit board including a metal bump according to an embodimentof the present invention. Hereinafter, the method of manufacturing aprinted circuit board including a metal bump according to an embodimentof the present invention will be described with reference to FIGS. 2 to11.

First, a process of applying a dry film 310 on a carrier 100 and thenpatterning the dry film 310 to form holes 315 for forming metal bumps500 will be described. In this embodiment, for example, a process ofplacing a printed circuit board on one side of the carrier 100 isdescribed, but a process of placing a printed circuit board on bothsides of the carrier 100 may be conducted.

As shown in FIG. 2, in order to prevent a printed circuit board fromwarping during processing, a carrier 100, functioning as a support, isprovided. For example, the carrier 100 has a structure in whichinsulation material layers 150 and release layers 170 are sequentiallyformed on both sides of a double-sided copper clad laminate in whichcopper foil layers 130 are formed on both sides of an insulation resinlayer 110.

In this case, in order to increase the strength of the double-sidedcopper clad laminate, the insulation resin layer 110 contains a glassmaterial, and may have a thickness of about 100˜800 μm.

Further, the release layer 170 has a length and an area smaller thanthose of the copper foil layer 130, and may be formed on the insulationmaterial layer 150, but not on the lateral sides of the copper foillayer 130. The release layer serves to easily separate metal foil 190from the carrier 100 in the latter half of a process of manufacturing aprinted circuit board. Meanwhile, the release layer 170 may be formed byapplying a releasing material on the insulation material layer 150 inthe form of thin film or sputtering the releasing material on theinsulation material layer 150. The metal foil 190, which is bound by aportion of the insulation material layer 150 on which the release layer170 is not formed, is applied on the carrier 100. The metal foil 190 maybe made of a conductive metal such as copper (Cu), gold (Au), silver(Ag) or the like. In this embodiment, copper foil is used as the metalfoil 190.

Thereafter, as shown in FIG. 3, a dry film 310 is applied on the carrier100 and then patterned to form holes 315 for forming metal bumps 500. Asthe dry film 310, a photosensitive dry-film may be used. The patterningof the dry film 310 may be performed by selectively exposing and curingthe applied dry film 310 using a mask (not shown) having light shieldingpatterns and then removing the uncured portion of the dry film 310.

Subsequently, as shown in FIG. 4, a connection metal layer 410 is formedon the bottoms of the holes 315. The formation of the connection metallayer 410 may be optional. The connection metal layer 410 may be formedusing the metal foil 190 as a lead wire by electrolytic plating. Theconnection metal layer 410 serves to protect the upper ends of the metalbumps 500 to be connected to an electronic part later and serve tosmoothly perform the electrical connection of the electronic part andthe metal bumps 500. The connection metal layer 410 may be made of aconductive metal such as tin (Sn), an alloy of tin (Sn) and silver (Ag)or the like. The connection metal layer 410 may be made of a metal whichcauses the copper foil formed on the carrier 100 to be selectivelyetched with respect to the connection metal layer 410.

Next, as shown in FIG. 5, a process of forming an upper circuit layer600 including metal bumps 500 charged in the holes 315 and connectionpads 630 on the dry film 310 will be described. First, a seed layer (notshown) is formed on the dry film 310 and the inner surfaces of theholes. Subsequently, a plating resist (not shown) made of aphotosensitive material is placed on the seed layer, and then the seedlayer is patterned to form openings for forming the upper circuit layer600, including openings for forming the connection pads 630, theseopenings exposing the holes 315. Subsequently, the upper circuit layer600 including metal bumps 500 charged in the holes 315 and theconnection pads 630 can be formed by electroplating the openings througha general SAP process. Then, the exposed portion of the seed layer isremoved by flash etching or quick etching. In this case, the uppercircuit layer may selectively include circuit patterns 610. It can beeasily understood that whether or not the circuit patterns 610 areformed can be determined by the patterning type of the plating resist.

In this case, the diameters of the holes formed by patterning the dryfilm 310 through exposure and development are constant. For this reason,it is possible to form the metal bumps 500 having a constant diameter,that is, having a post shape, lateral sides of which are not tapered.Here, the meaning that the metal bump 500 has a constant diameter doesnot mean that the upper and lower diameters of the metal bump 500 aremathematically exactly equal to each other but means that a slightchange in diameters of the metal bumps 500 due to the errors occurringin a substrate manufacturing process is allowed. Further, it can beunderstood that the metal bumps 500 may be formed to have a heightcorresponding to the thickness of the dry film 310.

Next, as shown in FIG. 6, a process of forming an insulation layer 700on the dry film 310 will be described. The insulation layer 700 may be asolder resist layer, and may be made of a composite polymer resin whichis generally used as an interlayer insulation material. For example, theinsulation layer 700 may be made of prepreg, or an epoxy resin such asFR-4, BT(Bismaleimide Triazine), ABF(Ajinomoto Build up Film) or thelike, but the present invention is not limited thereto.

Next, as shown in FIGS. 7 and 8, a process of forming a build-up layer800 including a lower circuit layer 830 on the insulation layer 700 willbe described. In this process, via holes are formed in the insulationlayer 700 using a YAG laser drill or a CO₂ laser drill, and then aninner circuit layer 810 is formed through a semi-additive process, andthen the lower circuit layer 830 is formed by repeating the aboveprocesses. In this embodiment, a process of forming a build-up layerincluding one inner circuit layer is exemplified, but the presentinvention is not limited thereto. The number of the inner circuit layers810 is not limited, and the inner circuit layer 810 may not exist. Whenthe lower circuit layer 830 is completed, a solder resist layer 850 forcovering the lower circuit layer 830 is formed on the lower circuitlayer 830.

Next, as shown in FIG. 9, a process of removing the carrier 100 will bedescribed. In this process, the lateral portions of the carrier 100 andthe printed circuit board placed on the carrier 100 may be cut through arouting process, and the metal foil 190 constituting an outer layer ofthe carrier 100 may be separated from the carrier 100. Here, the routingprocess is a process of performing mechanical cutting using a routingbit. In the routing process, the lateral portions of the carrier 100 andthe printed circuit board are cut and removed, and thus the insulationmaterial layer 150 binding the metal foil 190 applied on the carrier 100is also removed, thereby separating the metal foil 190 and the printedcircuit board from the carrier 100. Then, the metal foil is removed fromthe dry film 310 through an etching process.

Subsequently, as shown in FIG. 10, openings 855 for exposing lowerconnection pads formed in the lower circuit layer 830 are formed in thesolder resist layer 850.

Subsequently, as shown in FIG. 11, the dry film 310 is removed using astripping agent.

Thereafter, a surface protection layer may be formed on the exposedsurfaces of the metal bumps 500 and the connection pads 630. Forexample, the surface protection layer can be formed by performing an OSPprocess or by performing a nickel or gold plating process.

According to the above process of manufacturing a printed circuit board,since the dry film 310 is formed on the carrier 100 and then metal bumpsare formed, a printed circuit board including post-shaped metal bumpshaving constant heights and excellent electric conductivity can bemanufactured.

Further, according to the above process of manufacturing a printedcircuit board, since the metal bumps 500 are formed by charging a metalinto the holes 315 having constant diameters and formed in the dry film310 through a plating process, metal bumps having constant diameters canbe formed, and thus metal bumps arranged at fine pitches can also beformed.

FIGS. 12 to 22 are sectional views showing a method of manufacturing aprinted circuit board including a metal bump according to anotherembodiment of the present invention. Hereinafter, the method ofmanufacturing a printed circuit board including a metal bump accordingto another embodiment of the present invention will be described withreference to FIGS. 12 to 22. Here, parts of the description overlappingwith the above embodiment are omitted.

First, as shown in FIG. 12, a carrier 100 coated with metal foil 190 isprovided.

Subsequently, as shown in FIG. 13, a metal layer 330 including holes 335for forming metal bumps 500 is formed on the metal foil 190. The metallayer 330 may be formed by forming a photosensitive plating resist layer(not shown) on the metal foil 190 and patterning the photosensitiveplating resist layer using the metal foil 190 as a lead wire throughelectrolytic plating. The metal layer 330 may be made of a conductivemetal. In this embodiment, the metal layer 330 is made of copper (Cu).

Subsequently, as shown in FIG. 14, a barrier layer 430, serving as anetching inhibiting layer, is formed on the metal layer 330 and the innersurfaces of the holes. The barrier layer 430 may be formed byelectroless plating or electrolytic plating. In this case, the barrierlayer 430 may be made of a metal which has selective etchability withrespect to the metal layer 330 and the metal bumps 500 and upper circuitlayer 600 to be formed later. In this embodiment, the barrier layer 430is made of nickel (Ni).

Subsequently, as shown in FIG. 15, metal bumps 500 are formed in theholes 335 and an upper circuit layer 600 is formed on the barrier layer430, and then, as shown in FIG. 16, an insulation layer 700 is formed onthe upper circuit layer 600.

Subsequently, as shown in FIGS. 17 and 18, an inner circuit layer 810and a lower circuit layer 830 are sequentially formed on the insulationlayer 700, and then a solder resist layer 850 is formed on the lowercircuit layer 830.

Subsequently, as shown in FIG. 19, the metal foil 190 is separated fromthe carrier 190 and then removed.

Subsequently, as shown in FIG. 20, openings 855 for exposing lowerconnection pads formed in the lower circuit layer 830 are formed in thesolder resist layer 850.

Subsequently, as shown in FIG. 21, the metal layer 330 is etched andthus removed, and then, as shown in FIG. 22, the barrier layer 430 isremoved. The barrier layer 430 may be removed using a nickel selectiveetchant. The barrier layer 430 and the upper circuit layer 600 may bemade of metals, one of which has a selective etchability with respect tothe other. The barrier layer 430 can be removed without damaging theupper circuit layer 600.

As described above, the printed circuit board according to the presentinvention is advantageous in that the printed circuit board can beeasily connected electrically to an electronic part mounted thereinbecause the printed circuit board includes post-shaped metal bumpshaving excellent electric conductivity. Further, the printed circuitboard according to the present invention is advantageous in that theprinted circuit board includes metal bumps arranged at fine pitchesbecause the metal bumps have constant diameters, the lower diameters ofwhich are not larger than the upper diameters thereof.

According to the process of manufacturing a printed circuit boardaccording to the present invention, since a dry film is formed on acarrier and then metal bumps are formed, a printed circuit boardincluding post-shaped metal bumps having constant heights and excellentelectrical conductivity can be manufactured.

Further, according to the process of manufacturing a printed circuitboard of the present invention, since metal bumps 500 are formed bycharging a metal into holes having constant diameters and formed in adry film through a plating process, metal bumps having constantdiameters can be formed, and thus metal bumps arranged at fine pitchescan also be formed.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A printed circuit board, comprising: an upper circuit layer includingconnection pads made of a conductive metal and buried in an insulationlayer; and metal bumps, each having a constant diameter, which areintegrated with the connection pads and protrude over the insulationlayer.
 2. The printed circuit board according to claim 1, wherein eachof the connection pads has an exposed surface being flush with a surfaceof the insulation layer.
 3. The printed circuit board according to claim1, wherein the insulation layer is made of a solder resist.
 4. Theprinted circuit board according to claim 1, further comprising: aconnection metal layer formed on the metal bumps.
 5. The printed circuitboard according to claim 1, further comprising: a build-up layerincluding a lower circuit layer disposed beneath the insulation layer.6. The printed circuit board according to claim 5, wherein the lowercircuit layer includes lower connection pads, and wherein the printedcircuit board further comprises a solder resist layer covering the lowercircuit layer and having openings for exposing the lower connectionpads.
 7. A method of manufacturing a printed circuit board, comprising:applying a dry film on a carrier and then patterning the dry film toform holes for forming metal bumps; forming an upper circuit layerincluding metal bumps charged in the holes and connection pads on thedry film; forming an insulation layer on the dry film; forming abuild-up layer including a lower circuit layer on the insulation layer;removing the carrier; and removing the dry film.
 8. The method accordingto claim 7, wherein the forming of the upper circuit layer comprises:forming a seed layer on the holes and the dry film; patterning the seedlayer to form openings for forming the upper circuit layer, includingopenings for forming the connection pads, the openings exposing theholes; plating the openings for forming the upper circuit layer to formthe upper circuit layer including the metal bumps and the connectionpads; and removing the seed layer.
 9. The method according to claim 7,after forming the build-up layer, further comprising: forming a solderresist layer on the lower circuit layer after the forming of thebuild-up layer.
 10. The method according to claim 7, wherein theremoving of the carrier comprises: separating a metal foil constitutingan outer layer of the carrier from the carrier; and removing the metalfoil from the dry film.
 11. The method according to claim 7, afterapplying the dry film and patterning the dry film, further comprising:forming a connection metal layer on bottoms of the holes after theapplying of the dry film.